Re: [PATCH 1/8] execmem: drop unused execmem_update_copy()

[Mike Rapoport]

On Mon, Jul 07, 2025 at 12:10:43PM +0200, Christophe Leroy wrote:
> 
> Le 04/07/2025 à 15:49, Mike Rapoport a écrit :
> > From: "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx>
> > 
> > The execmem_update_copy() that used text poking was required when memory
> > allocated from ROX cache was always read-only. Since now its permissions
> > can be switched to read-write there is no need in a function that updates
> > memory with text poking.
> 
> Erm. Looks like I missed the patch that introduced this change.
> 
> On some variant of powerpc, namely book3s/32, this is not feasible.

The only user of EXECMEM_ROX_CACHE for now is x86-64, we can always revisit
when powerpc book3s/32 would want to opt in to cache usage.

And it seems that [MODULES_VADDR, MODULES_END] is already mapped with
"large pages", isn't it?

> The granularity for setting the NX (non exec) bit is 256 Mbytes sections.
> So the area dedicated to execmem [MODULES_VADDR; MODULES_END[ always have
> the NX bit unset.
> 
> You can change any page within this area from ROX to RWX but you can't make
> it RW without X. If you want RW without X you must map it in the VMALLOC
> area, as VMALLOC area have NX bit always set.

So what will happen when one callse

	set_memory_nx()
	set_memory_rw()

in such areas?

> Christophe

-- 
Sincerely yours,
Mike.